This invention relates to a shaft seal and more particularly to a one-piece shaft seal which effectively functions as both a seal and a bushing for the shaft.
The seal of this invention functions as a replacement for conventional packing elements, which also act as both the seal for the shaft and the bushing for the shaft. The conventional packing elements are used by forcing them into a housing and compressing them with an adjustable retainer. This process, by its nature, creates a tradeoff situation. The greater the compression from the retainer, the better the packing will seal the shaft. Unfortunately, the greater the compression, the more difficult it is to rotate the shaft in the packing.
A happy medium must be reached in order for the assembly to operate properly. If the packing is too tight, it builds excessive heat from the friction, assuming that the drive has enough power to turn the shaft. In the event the packing is too loose, the seal leaks while the shaft is able to wobble. The "happy medium" is reached only after trial and error has found the best compression. And even then, the packing must be installed, run-in to seat the packings, and then retightened.
The one-piece seal of this invention eliminates the problematic steps that are associated with the use of packings. This is accomplished by having the seal be both the seal and the bushing. The center section of the seal is the proper diameter to be the bushing that is required to support the shaft during operation. While the ends of the seal have a lip seal geometry built into them that allows the seals to stetch over the shaft during installation. This stretch provides the necessary radial compressive force required to effect a seal in both static and dynamic modes. The stretch is possible because a groove in each end of the seal enables the seal ends to expand to the size of the shaft while the diameter of the bushing area of the seal remains constant.
The seal of this invention may require cleaning after use. However, the process of cleaning and changing the seal of this invention compared with a packing type seal is much simpler, faster, less expensive, and less likely to be done incorrectly. The woven packing absorbs product between its fibers. Since there is no way to see inside the packing to check for product that may still be in a clean packing, the packing must simply be replaced in order to guarantee that there is no contamination in the next useage.
The one-piece seal can be cleaned with the same automatic equipment that cleans the other parts of the tank in which the seal is installed. A simple visual inspection clearly shows if the seal is clean or not. If clean, install. If not, either install with the contaminated end away from the product or replace the seal. Replacing the seal requires none of the run-in and re-adjustment that is required of the packing. Once installed, it is ready to use immediately.
Specifically, the seal made in accordance with the preferred embodiment of this invention has an annular hollow body which defines a bushing cavity therein and which further defines a lip seal portion and flexure grooves at each end thereof. The lip seal portion and flexure grooves co-operate to allow the secure containment of the shaft within the containment cavity and provides effective sealing force even when the shaft is not perfectly straight. The entire shaft seal assembly is disposed within a receiving member which prevents communication between the seal and the contained material. Therefore the seal may not need to be cleaned after different materials are placed within the container.
These and other aspects, features, advantages, and objects of this invention will be more readily understood upon reviewing carefully the following detailed description in conjunction with the accompanying drawings and appended claims.